When solving any truss, the reaction forces at each support should be determined before trying to calculate individual member loads. Starting with a FBD of the entire truss, the basic moment equilibrium equation gives,

     ΣM₁ = 0
     2.5(4/3 + 4) + 5(4/3 + 4) + 7.5(4/3 + 4) - 10R = 0
     R = 8.0 kips

Due to symmetry, the reaction forces at both the left and right wall are equal,

     R_L = R_R = R = 8 kips

With the reactions known, it is now possible to analyze joint 1. Note that both F₃₁ and F₂₁ are drawn away from the joint, representing tension.

The two unknowns forces, F₃₁ and F₂₁, can be found using the two force equilibrium equations,

     ΣF_x = 0
     - F₂₁ - F₃₁ cos40 = 0

     ΣF_y = 0
     F₃₁ sin40 + R = 0

Substituting known values and solving gives,

     F₃₁ = -8/sin40 = -12.45 kips
     F₂₁ = -F₃₁ cos40 = 9.534 kips

The value of F₂₁, 9.534 kips, was determined at joint 1 and can now be used at joint 2.

The force in member F₃₂ is easy to determine since all members and loads are perpendicular. Summing the forces in the vertical gives,

     ΣF_y = 0
     F₃₂ = 1.333 kips

Since there are only two horizontal member forces, they must be equal,

     ΣF_x = 0
     F₂₁ = F₄₂ = 9.534 kips

The value of  F₃₁, -12.45 kips, and F₃₂, 1.333 kips, were determined from joint 1 and joint 2, respectively. It is now possible to determine forces, F₅₃ and F₄₃, at joint 3,

     ΣF_x = 0 = cos40 [-F₅₃ - F₄₃ + (-12.45)]
     F₅₃ = -F₄₃ - 12.45

     ΣF_y = 0 = sin40 [F₅₃ - F₄₃ - (-12.45)] - 4 - 1.333

Eliminating F₅₃ gives,

     0 = -2F₄₃ - 4/sin40 - 1.333/sin40 
     F₄₃ = -4.148 kips

and

     F₅₃ = 4.148 - 12.45 = -8.302 kips

Now that F₄₂, 9.534 kips, and F₄₃, -4.148 kips, are known, joint 4 can be analyzed. Due to symmetry, the left member forces are the same as the right member forces. There is only one unknown force, F₅₄. Using ΣF_y = 0 gives, 

     F₅₄ + 2(-4.148) sin40 - 1.333 = 0
     F₅₄ = 6.666 kips

As shown by the force diagram, the largest tensile force is 9.534 kips and the largest compressive force is -12.45 kips.

The best truss angle, θ, that minimizes the member loads can be determined by using the truss simulation. The best angle is the largest angle possible in the simulator, 65^o. Thus a steep truss reduces the load. However, the cost is higher and buckling problems will also need to be considered.